This invention relates to epoxy resin-based water-reducible coating compositions. In a specific embodiment, the invention relates to the stabilization of nitroparaffin compositions which have utility in modified polyaminecured epoxy resin coating formulations.
High-performance coatings for protection of metal surfaces of ships, aircraft, bridges, large liquid containers, and other structures exposed to corrosive environments must be resistant to the corrosive effects of water and solvents. Excellent coating properties can be obtained from the use of solvent-borne, two-package epoxy coatings. The use of organic solvents in coating formulations is increasingly restricted, however, by air-quality regulations controlling the volatile organic content (VOC) of solvent-borne coatings.
The need for low-VOC coating formulations has led to the development of water-dispersible epoxy coating formulations in which a portion of the organic solvent is replaced with water. However, conventional amine-cured epoxy systems are not readily water-dispersible. The addition of surfactant-type emulsifying agents is undesirable because such agents tend to remain in the coating and adversely affect coating properties. It has been found that epoxy systems containing amino-functional curing agents modified to have emulsifying properties are more readily water-dispersible. Such modified polyamine curing agents, however, have a short pot life. The pot life of modified polyamine resin curing agents has been lengthened by addition of a nitroparaffin to the coating system. Such nitroparaffin-containing systems exhibit good coating properties and water-dispersibility, but premixed epoxy/nitroparaffin solutions used to prepare the water-dispersible coating formulations have a tendency to darken in color and gel with prolonged storage, particularly at temperatures encountered during hot weather storage.
It is therefore an object of the invention to provide nitroparaffin-containing formulations which have good storage stability.